How do I model from a side view with a reference image?
You need to use background images either in orthographic view, or using stationary camera views rather than planes. Background images is in the properties window on the right hand side when you're in 3D view (you can toggle its view with the "n" key). from there you can load up images, and choose which views they are visible from. all views except for camera view are only visible in orthographic mode which is the view when you press 5 on the num pad and then press 1, 3, or 7 to see front, side, or top views. since things are not orthographic in real life you can also use a camera view background image to keep the reference image stationary against the  model.